Purification of 1,1,1,3,3-pentafluorobutane

ABSTRACT

In the synthesis of 1,1,1,3,3-pentafluorobutane (R-365mfc), a mixture of R-365mfc and the impurity 1-chloro-3,3,3-trifluoropropene (R-1354zd) is purified and R-1354zd is removed from the mixture by contacting the mixture with 1-5 mols of chlorine for each mol of R-1354zd in the presence of ultraviolet light having a wavelength between about 300 to 400 nm which provides at least 0.02 watts-hour/kg of the mixture. The R-1354zd is reduced to below 10 wt. ppm as it is converted to 2,3-dichloro-1,1,1,3-tetrafluorobutane (R-354) or other butane containing more chlorine and having a higher boiling point than R-365mfc. The butane(s) may be separated more easily from R-365mfc. The photochlorination is effected in a manner such that at least about 96 weight percent of the starting amount of R-365mfc is maintained in the mixture.

BACKGROUND OF THE INVENTION

[0001] This invention relates principally to the purification of1,1,1,3,3-pentafluorobutane, also designated R-365mfc, which has been ofparticular interest as a replacement for chlorofluorocarbons andhydrochlorofluorocarbons having similar physical properties, forexample, 1,1,2-trichloro-1,2,2-trifluoroethane (R-113),fluorotrichloromethane (R-11) and 1,1-dichloro-1-fluoroethane (R-141b).

[0002] R-365mfc may be prepared by a two-step process involving theaddition of carbon tetrachloride to 2-chloroprene to produce1,1,1,3,3-pentachlorobutane (R-360) in the presence of a copper salt andan amine followed by fluorination with hydrogen fluoride as disclosed inU.S. Pat. No. 5,917,098.

[0003] It is characteristic of such reactions that many by-products areformed, containing varying numbers of hydrogen, chlorine, and fluorineatoms on C₁-C₄ compounds. These by-products and the unreacted feedmaterial may be separated by distillation where possible. Some compoundsare relatively harmless since their presence does not greatly alter thephysical properties for which R-365mfc is useful. One by-product whichmust be removed because of its toxicity is 1,1,1,3-tetrafluoro-2-butene(R-1354zd), although only relatively small amounts are typically presentin R-365mfc as formed. R-1354zd has a boiling point close to that ofR-365mfc making them difficult to separate by distillation. Afterdistillation of the crude product, R-1354zd will still be present inamounts from about 300 to 20,000 wt. ppm. It should be reduced to belowabout 100 wt. ppm due to the potential toxicity of unsaturatedcompounds. Preferably, the amount of R-1354zd should be reduced to 20ppm (wt.) and most preferably below about 10 wt. ppm.

[0004] Further improvement in methods of purifying R-365mfc,particularly with respect to eliminating R-1354zd, is desired and thepresent inventors have discovered a means for purification byphotochlorination.

[0005] It is advantageous also to remove other unsaturated by-productsthat can be present in the R-365mfc reaction product, including, forexample, R-1353 and the like.

SUMMARY OF THE INVENTION

[0006] Unsaturated by-products including R-1354zd are removed from amixture consisting substantially of R-365mfc and containing up to about20,000 wt. ppm R-1354zd by contacting the R-365mfc mixture with 1-5moles of chlorine for each mole of R-1354zd in the presence ofultraviolet light having a wavelength between about 300 to 400 nm whichprovides at least 0.02 watts-hour/kg of the mixture, preferably 0.02 to2.0 watts-hour/kg. The R-1354zd can be reduced to below 10 wt. ppm orlower as it is converted to 2,3-dichloro-1,1,1,3-tetrafluorobutane(R-354) or other butanes containing more chlorine such as2,2,3-trichloro-1,1,1,3-tetrafluorobutane (R-344) or 2,2,3,4-tetrachloro1,1,1,3-tetrafluorobutane (R-334), which have higher boiling points andcan be easily separated from R-365mfc. Other unsaturated compounds, suchas 3-chloro-1,1,1-trifluoro-2-butene (R-1353), are also removed bychlorination to other derivatives that can be separated, for example, bydistillation. The temperature and pressure used may be adjusted toprovide R-365mfc in either the vapor or liquid phase, the vapor phasebeing preferred.

[0007] An advantage of the photochlorination of the present invention isthat it does not affect materially the desired R-365mfc product. Thus,while a high proportion of the R-1354zd impurity is in effect removed bythe photochlorination, a substantially high proportion of the R-365mfcis maintained. For example, the photochlorination can be effected in amanner such that at least about 96 weight percent, preferably at leastabout 98 wt. %, of the starting amount of R-365mfc is maintained in themixture. This is indeed surprising when it is considered that theproportion of R-365mfc in the starting mixture is high, for example, atleast about 98 weight percent.

DETAILED DESCRIPTION OF THE INVENTION

[0008] R-365 may be produced by the process of U.S. Pat. No. 5,917,098,beginning from carbon tetrachloride and 2-chloroprene. The crude productwill contain a variety of by-products. It is of particular importance toremove 1,1,1,3-tetrafluoro-2-butene (R-1354zd) from the crude product.Preliminary separation of R-365mfc by distillation will leave about 300to 20,000 wt. ppm of R-1354zd having a boiling point of about 16° C.compared to 40° C. for R-365mfc, the difference in boiling points makingR-1354zd difficult to separate from R365mfc. In the process of theinvention, R-1354zd or other unsaturated compounds which may be present,for example, 3-chloro-1,1,1-trifluoro-2-butene (R-1353), are reactedwith chlorine to provide more highly chlorinated compounds which have ahigher boiling point and can be readily separated from R-365mfc.

[0009] As mentioned above, the photochlorination may be effected so thatat least about 96% (based on weight amount) or more of the desiredstarting amount of R-365mfc is maintained in the mixture, i.e. notaffected by the photochlorination.

[0010] In the process, crude R-365mfc containing about 300 to 20,000 wt.ppm of R-1354zd along with minor amounts of other by-products such asthose mentioned above will be contacted with chlorine in the presence ofultraviolet light having a wavelength of about 300 to 400 nm. It shouldbe understood that an ultraviolet lamp may have radiation outside thisrange also, but that photochlorination requires UV light within thisrange.

[0011] The ultraviolet light will have an intensity which provides anexposure greater than zero and at least about 0.02 watts-hour/kg of theR-365mfc mixture, preferably 0.02 to 2.0 watts-hour/kg.

[0012] The ultraviolet light may be provided by arc lamps includingmercury, argon, or xenon and filament lamps including tungsten andhalogen.

[0013] Chlorine is introduced into the crude R-365mfc stream at a ratesufficient to provide about 1 to 5 moles of chlorine for each mole ofR-1354zd, preferably about 1 to about 1.5. It has been found thatincreasing either the ratio of chlorine to R-1354zd (Cl₂/R-1354zd) orthe ultraviolet light exposure improves the chlorination of R-1354zd.Generally, we have been able to reduce the R-1354zd to below 10 wt. ppmusing a UV exposure above about 0.04 watts-hour/kg but with quite lowratios of Cl₂/R-1354zd. Conversely, much lower UV exposures can be usedif higher Cl₂/R-1354zd ratios are used. The Cl₂/R-1354zd ratio and UVexposure may be adjusted to provide the desired set of conditions.

[0014] The temperature employed may vary but may be from about −50° C.to 200° C., preferably about 25° to 60° C.

[0015] The pressure selected will be a convenient value to suit theprocessing conditions for R-365mfc and to assure that R-365mfc is aliquid or vapor, as desired.

[0016] The UV radiation from a lamp ordinarily will be expressed aswatts, which is a rate of delivering energy. For present purposes, it isconsidered more useful to express radiation as the quantity of energydelivered over a period of time, i.e. the “exposure,” rather than as therate. Thus, the exposure may be expressed as watts-hours, which isrelated to the number of photons of energy delivered and theirwavelength and these, in turn, relate to the chlorination of unsaturatedmolecules such as R-1354zd. Since the exposure is the product of therate of delivering energy (photons/time) and the time, it will be clearthat either the rate or the time could be varied. However, for practicalapplications the rate and the time will have limits imposed by the needto carry out the desired photochlorination reaction within constraintsof time and product yield. If a high rate or a long time is used, notonly will R-1354zd be chlorinated to R-354 (or R-344 or R-334), but alsochlorine will react with other molecules, particularly with R-365mfc tomake 2-chloro-1,1,1,3,3-pentaflurobutane (R-355mdc). Alternatively, if avery low rate, or a short time, is used then insufficient chlorinationof R-1354zd would be expected. Increasing the ratio of chlorine toR-365mfc will tend to increase the production of R-355mdc. Conditionswhich involve a UV exposure of about 1.5 to 5.0 watts-hour/kg ofR-365mfc and a Cl₂/R-1354zd molar ratio of greater than about 1.5:1 andup to about 50:1 will tend to result in increased production ofR-355mdc.

[0017] As illustrated in the examples, the photochlorination can beeffected in a batch process or a continuous process.

[0018] After the R-365mfc-containing mixture has been photochlorinated,the chlorinated products may be separated from the R-365mfc, forexample, by distillation, since the boiling points are no longer closeto that of R-365mfc. For example, the boiling points of R-354, R-344,R-334 and other chlorinated butanes that are typically produced in thephotochlorination are at least about 40° C. above the boiling point ofR-365mfc (40° C.). To exemplify, the boiling points of R-354 isomers areestimated to be about 83° C.; the boiling points of R-344 isomers areestimated to be about 120° C.; and boiling points of R-334 isomers areestimated to be about 155° C. The boiling point of R-355 is estimated tobe about 48° C. (The boiling points referred to in this specificationare at one atmosphere pressure.) Separation of the Cl-containingby-products can be effected readily by conventional distillation. Anyresidual chlorine, HCl or HF may be separated by absorption of chlorinein aqueous caustic, by adsorption on carbon molecular sieves, orreaction with aqueous sodium sulfite or sodium thiosulfate.

EXAMPLES Example 1 Liquid Phase Purification of R-365mfc

[0019] The photochlorination of R-365mfc is carried out in a 125 mLPyrex pressure vessel equipped with a dip leg inlet and a pressuregauge. This vessel is chilled in ice water and 20.0 grams of impureR-365mfc containing 0.08% R-1354zd is condensed into it. Then, whilestill cold, a stream of chlorine gas is passed at 10 mL/min through thissolution for about 52 seconds. We calculate according to the ideal gaslaw that this should correspond to 3.6×10⁻⁴ moles of chlorine, or a 1:1mole ratio with the R-1354zd impurity. The vessel is then allowed towarm to room temperature.

[0020] The reactor vessel is placed for 5 minutes at the focus ofRPR-100 Rayonet reactor (Southern New England Ultraviolet Company)equipped with 16 RPR-3500 lamps having their peak intensity at awavelength of 350 nm. The Pyrex walls of the pressure vessel removelight below 300 nm. Ferrioxalate actinometry is used to measure theradiation received (see The Chemists Companion, A. J. Gordon & R. A.Ford, Wiley Interscience (1972), pages 362-368). In this vessel underthese conditions this procedure gives an incident light intensity of1.317×10⁻⁷ Einstein/sec (0.0417 watts). One Einstein is equal to a molof photons. A five minute exposure should therefore supply 3.95×10⁻⁵Einsteins of light (0.039 watt-hour/kg). After exposure, the vapor headof the pressure vessel is sampled by gas chromatography.

Example 2 Vapor Phase Purification of R-365mfc

[0021] The photochlorination of R-365mfc is carried out in a 125-mLPyrex pressure vessel equipped with an inlet at the bottom and an outletat the top. The reactor vessel is placed at the focus of RPR-100 Rayonetreactor (Southern New England Ultraviolet Company) equipped with 16RPR-3500 lamps having their peak intensity at a wavelength of 350 nm.The Pyrex walls of the pressure vessel remove light below 300 nm. Thevessel is immersed in a Pyrex constant temperature bath held at 59° C.to ensure that the R-365mfc remains in the vapor phase.

[0022] Two feed streams are passed through separate lengths of capillarytubing and then mixed and passed into the reactor at 5 psig (34.5 kPagauge). The impure R-365mfc contains 0.08% R-1354zd plus otherimpurities. One stream contains impure R-365mfc while the secondcontains chlorine. By blending the two streams the ratio of chlorine toR-1354zd is varied. The radiation exposure is calculated from theresidence time and the light intensity and varies from 2 to 3.5watts-hour/kg. After exposure to the ultraviolet light the productstream is analyzed by gas chromatography using the procedures of Example1.

[0023] It is observed that, as the molar ratio of chlorine to R-1354zdis increased from 0.1 to about 1.5, the concentration of R-1354zd, andof the other olefins is reduced from their feed concentrations toconcentrations below the detection limit (10 ppm). In proportion to thedecrease in R-1354zd and the other olefins, the correspondingchlorinated products are observed to increase. At the molar ratiocorresponding to an R-1354zd concentration of about 100 ppm (i.e. amolar ratio near 1.0), the concentration of R-355mdc is observed tobegin increasing with increasing molar ratio.

1. A process for removing 1-chloro-3,3,3-trifluoropropene (R-1354zd) orother olefinic impurities from 1,1,1,3,3-pentafluorobutane (R-365mfc) byphotochlorination comprising (a) contacting a mixture consistingsubstantially of a predetermined weight amount of R-365mfc and up toabout 20,000 wt. ppm R-1354zd with about 1-5 mols of chlorine for eachmol of R-1354zd or other olefins in the presence of ultraviolet lighthaving wavelengths between about 300 and 400 nm providing an exposuregreater than zero and at least about 0.02 watt-hour/kg of said mixture,said photochlorination being effective to reduce the concentration inthe mixture of R-1354zd or other olefins to less than 100 wt. ppm byconverting said R-1354zd to 2,3-dichloro-1,1,1,3-tetrafluorobutane(R-354) or other butane which contains greater amounts of chlorine, asat least about 96% of said predetermined weight amount of R-365mfc ismaintained in the mixture; and (b) separating the R-354 or other butaneformed in (a) from R-365mfc.
 2. A process according to claim 1 whereinthe boiling point of said R-354 or other butane is at least about 40° C.above the boiling point of said R-365mfc and separating the R-365mfc andthe R-354 or other butane by distillation.
 3. The process of claim 1effected as a batch process.
 4. The process of claim 1 wherein saidultraviolet light provides an exposure of about 0.02 to 2 watts-hour/kgof said mixture.
 5. The process of claim 1 wherein about 1 to about 1.5mols of chlorine are present for each mol of R-1354zd.
 6. The process ofclaim 1 wherein the contacting of (a) is carried out at a temperatureand a pressure sufficient to assure that R-365mfc is liquid.
 7. Theprocess of claim 1 wherein the contacting of (a) is carried out at atemperature and a pressure at which R-365mfc is vapor.
 8. The process ofclaim 1 wherein the temperature is in the range of about −50° C. to 200°C.
 9. The process of claim 8 wherein the temperature is in the range ofabout 25° C. to 60° C.
 10. The process of claim 1 wherein the separationof (b) is carried out by distillation.
 11. The process of claim 1wherein said other olefinic impurities comprise R-1353.
 12. The processof claim 1 effected as a continuous process.